From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The failure of a Duralumin connecting rod during a 100-hour endurance test on a Bentley B.6 unit.
| Identifier | ExFiles\Box 85\3\ scan0082 | |
| Date | 11th April 1934 | |
| 11.4.34. FAILURE OF DURAL CON. ROD - BENTLEY. We have recently had a failure of a Dural Con. Rod on the test bed. The failure occurred 5½ hrs. after the start of an attempted 100 hours endurance test at 4000 r.p.m. full throttle on a Bentley unit (B.6). The con. rods concerned were to EX.13352 in R.R.56 material, had reduced width of big end bearing and 0.002" clearance on dia. when cold. The running to which these rods had been subjected up to the time of failure was as follows :- 17½ hrs. F.T. Piston endurance running at 4000-4500 r.p.m. No. 5 big end seized due to oil supply failure. Replaced by new rod. Clearance of all rods increased from original of 0.0005"-0.001" to 0.002". 1 hour continuous F.T. endurance at 4500 r.p.m. Rods satisfactory. 5½ hours continuous F.T. endurance at 4000 r.p.m. No. 1 Rod Cap failed. No. 2 " " cracked. Total running at and over 4000 r.p.m. = 24 hrs. All rods were chalk tested for cracks after the failure of No. 1. No. 2 rod cap was found to be cracked as shown on Hs.{Lord Ernest Hives - Chair} 1353 attached. The fractured rod is shown by the attached photographs. From the appearance of the fractures it is evident that the original failure occurred at X as this is a typical fatigue fracture. The bearing surfaces of all rods were in extremely good condition after the 24 hours running. No Big End knocks could be detected on the test bed at low speeds with the 0.002" clearance although there appeared to be more noise at high speeds. With the original clearance of 0.0005-0.001" the oil pressure was 27 lbs/sq.in. at 4000 r.p.m. with the oil inlet to bearings at 90°C. With the 0.002" clearance this | ||